Plants effective anti-cancer agents, and it is significant

Plants have a long history
of use in the treatment of cancer (Hartwell, 1982).  Hartwell lists more than 3000 plant species
that have reportedly been used in the treatment of cancer, but in many
instances, the “cancer” is undefined, or reference is made to conditions such as
“hard swellings” tumors, to name a few. Such symptoms would generally apply to
skin, “tangible”, or visible conditions, and may indeed sometimes correspond to
a cancerous condition, but many of the claims for efficacy should be viewed
with some skepticism because cancer, as a specific disease entity, is likely to
be poorly defined in terms of folklore and traditional medicine. This is in
contrast to other plant-based therapies used in traditional medicine for the
treatment of afflictions such as malaria and pain, which are more easily defined,
and where the diseases are often prevalent in the regions where traditional
medicine systems are extensively used. Nevertheless, despite these
observations, plants have played an important role as a source of effective
anti-cancer agents, and it is significant that over 60% of currently used
anti-cancer agents are derived in one way or another from natural sources,
including plants, marine organisms and micro-organisms (Cragg
et al., 2005).


Plant-derived anti-cancer agents in clinical use:


The first agents to
advance into clinical use were the

So called vinca alkaloids,
vinblastine (VLB) and vincristine

(VCR), isolated from the
Madagascar periwinkle, Don. (Apocynaceae), which was used by various cultures
for the treatment of diabetes (Gueritte and Fahy,

2005). While
under investigation as a source of potential oral hypoglycemic agents, it was
noted that extracts diminish white blood cell counts and caused bone marrow
depression in rats, and subsequently they were found to be active against lymphocytic
leukemia in mice. This led to the isolation of VLB and VCR as the active
agents, so their discovery may be indirectly attributed to the observation of an unrelated medicinal use of the source plant. It is
interesting to note that though the plant was
originally endemic to Madagascar,the samples used in the discovery of VLB and
VCR were collected in Jamaica and the
Philippines. More recent semisynthetic analogs
of these agents are vinorelbine (VRLB) and vindesine
(VDS). These agents are primarily used in combination
with other cancer chemotherapeutic drugs for the
treatment of a variety of cancers, including leukemias, lymphomas, advanced testicular cancer, breast and lung



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